The aim of the proposed is to gain a further understanding of the physiologic importance of changes in the number and affinity of angiotensin II receptors as they relate to alterations in the hormonal responsiveness in several target tissues for angiotensin II. Because it is now apparent from recent studies of interactions between potassium and angiotensin II receptors that reciprocal changes occur simultaneously in different target tissues, it is relatively important to include as many easily assessable angiotensin II target tissues as possible when doing such receptor studies. The studies as outlined will therefore involve simultaneous evaluations of angiotensin II receptors of vascular and non-vascular smooth muscle, isolated renal glomeruli and adrenal glomerulosa. We will study the interactions of changes in physiologic balance that are known to be associated with altered responses to angiotensin II, but for which the precise mechanisms of altered responsiveness have remained obscure. Some of the conditions will include evaluations of the effects of changes in potassium balance, nephrectomy, ureteral ligation and changes in blood levels of angiotensin II. A radioreceptor assay adapted for smooth muscle, glomeruli and adrenal glomerulosa will be utilized to quantitate changes in number and affinity of angiotensin II receptors. To assess the physiologic relevance of any alterations in receptor number and affinity or both, parallel studies of target tissue responsiveness to angiotensin II will be included. These studies will include evaluations of pressor, smooth muscle, akdosterone and renal glomerular responsiveness to angiotensin either in vivo or in vitro. These studies will be performed in the rat since this species has been frequently used to assess the significance of physiologic variations on responses of different target tissues to angiotensin II.